- A program or device that can be used to acces the web. This includes browsers, web robots, intelligent agents, advanced hardware, specialized software, and so on
- A "reasonable" user agent -- one that provides support for core W3C standards
- A somewhat reasonable user agent supports HTML 3.2; a reasonable one supports at least HTML 4.0 and CSS level one.
- Web browsers that don't provide support for HTML 3.2 are at best broken software